In an uplink of 3rd Generation Partnership Project Long-Term Evolution (3GPP LTE) (hereinafter, referred to as LTE), a sounding reference signal (SRS) is used to measure reception quality (see NPLs 1 and 2).
The SRSs transmitted from terminals are multiplexed in a time-division, frequency-division, or code-division manner, In addition, an SRS is transmitted at periodic intervals. Particularly, when SRSs are code-division multiplexed in the same time/frequency, an orthogonal cyclic shift sequence is used. Hereinafter, the resources which are specified by time, frequency, and code and to which the SRSs are mapped may be referred to as SRS resources.
Methods of transmitting an SRS are classified into wideband transmission and narrowband transmission. In wideband transmission, the SRS is transmitted through a wide band at one point of time. In narrowband transmission, the SRS is transmitted through a narrow band at one point of time. Therefore, employing frequency hopping in the narrowband transmission and sequentially changing the transmission band enables an SRS transmission at a band equivalent to a wide band (see FIG. 1) Parameters necessary for transmitting the SRS (that is, SRS parameters) are notified as broadcast information or RRC control information to a terminal from a base station in an upper layer. The SRS parameters include an SRS transmission band, an SRS transmission interval, a cyclic shift number of a cyclic shift sequence multiplied by the SRS, and the like.
In LTE-Advanced (hereinafter, referred to as LTE-A), Single User-Multiple Input Multiple Output (SU-MIMO) is a communication system that uses 4×4 transmitting and receiving antennas and has been studied as a communication system applied to an uplink. Employing this MIMO communication system can enhance a data rate. When the MIMO system is employed, it is necessary to estimate channels of antennas of an antenna pair including a transmitting antenna and a receiving antenna. That is, when the MIMO system is employed, it is necessary to transmit the SRSs from. the transmitting antennas in a time-division, frequency-division, or code-division manner.